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COR and BBCOR Designs – Ensuring Safe Playing Environment

Today, we’re diving into a topic that combines the worlds of science and baseball in a way that might just change how you look at the game. I’m talking about the Coefficient of Restitution (COR) and its cousin, Batted Ball Coefficient of Restitution (BBCOR). They are crucial to understanding what makes baseballs, and indeed all of baseball, tick. Imagine sitting in the dugout with a seasoned MLB coach who’s also a bit of a science whiz. Ready? Let’s swing into it.

What is COR?

Ever wondered what gives a baseball that explosive “pop” off the bat? The answer lies in an often overlooked physics principle called the coefficient of restitution (COR).

The COR is essentially a measure of how “bouncy” or lively a ball is. It represents the ratio of a ball’s speed after a collision versus its speed before impact. This dimensionless value falls between 0 and 1, with 1 being a perfectly elastic collision where no energy is lost (by the way, there are no baseballs with COR value of 1).


Another way of looking at is when a car gets into an accident. Cars from 1970s-1980 were built like tanks: large and imposing. In car crashes, it maintained its shape to the detriment to passengers because the force from the crash was transferred to human bodies (high COR value). In contrast, modern cars are designed to “crumple”, absorbing all that impact energy to protect the occupants (low COR value).

To increase or reduce the COR value in baseballs, elastic and inelastic collisions models are used to differentiate in how much kinetic energy is conserved when a baseball collide with a bat.

In an elastic collision, the total kinetic energy remains constant as objects simply bounce off each other, characterized by a coefficient of restitution of 1. Conversely, an inelastic collision sees kinetic energy lost to other forms like heat or sound, with objects sticking together or deforming upon impact and a coefficient of restitution of 0.

baseball being hit by a bat -v5-final-fl

The primary determining factor of COR value for baseballs is the pill or core of a baseball.

What is BBCOR?

BBCOR is a standard that prescribes how much energy should be lost to reduce the “Trampoline Effect” when a bat makes contact with the baseball. As of March 2024, the National Federation of State High School Associations (NFHS) and National Collegiate Athletic Association (NCAA) based in the USA mandates that the maximum trampoline effect of a BBCOR bat will be 0.50. All BBCOR bats can be expressed as BBCOR 0.50 or “drop 3”, “-3”.


Baseball bats for younger groups typically will use the USABat standard which has been de-tuned to perform like a wood bat, hence there is no official BBCOR rating on these bats.

Cracking the Calculation

Focusing back to the ball itself, you don’t need a Ph.D. in Physics to calculate the COR value. Imagine you’re pitching a ball at 90 mph towards a wall, and it bounces back at 45 mph. The COR would be 0.5 (that’s 45 divided by 90). Simple, right? This little number tells us a lot about the ball’s liveliness. The higher the COR, the livelier the ball – it’s got more pep, more bounce, and yes, it’ll fly further when hit.

High Speed Camera NCAA baseball  being hit by a bat

The Science of Play

When it comes to ensuring that all equipment is up to snuff, there’s a whole world of testing and standards. ASTM standards like F1887 and F2845 lay down the law for measuring COR and dynamic stiffness of baseballs and softballs. These tests ensure that the balls used in play behave consistently, keeping the playing field level for all​.

Interestingly, did you know that even the air in the ballpark can affect COR? It’s true. Studies have shown that baseballs stored in high humidity conditions can have a lower COR, meaning they won’t fly as far. It’s a fascinating insight into how even the environment can play a role in the game’s dynamics​ (AIP Publishing)​.

Final Thoughts

The Coefficient of Restitution (COR) is indeed crucial in youth baseball. COR measures the “bounciness” of a baseball, indicating how much kinetic energy is retained when the ball hits a bat or another surface. A higher COR means the ball can bounce off the bat more energetically, potentially traveling further. This is beneficial for players looking to hit home runs. However, it also presents a safety hazard, especially for younger, less experienced players who might not react quickly enough to a fast-moving ball.

Standards and testing are essential to balance the benefits of performance with safety, ensuring no player has an undue advantage and minimizing risks on the field. I highly recommend that you my post, “Types of Baseball Cores – From Rubber to Cork Pills“, which offers valuable insights into the different materials used in baseball cores and how they affect the game’s dynamics and safety.

Understanding the variations can help coaches, parents, and players make informed decisions about the equipment best suited for young athletes’ skill and safety levels.

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